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41.
42.
Huseyin Sehitoglu Tracy Smith Xinlin Qing Hans J. Maier J. A. Allison 《Metallurgical and Materials Transactions A》2000,31(1):139-151
The stress-strain behavior of cast 319-T6 aluminum-copper alloys with three different secondary dendrite arm spacings (SDASs)
was studied at high temperatures and under thermomechanical deformation, exposing marked cyclic softening. A two state-variable
unified inelastic constitutive model proposed earlier was modified to describe the stress-strain responses of these alloys
by considering the variation of hardening and recovery functions of back-stress and drag stress. The SDAS was incorporated
in the model as a length-scale parameter, and the material constants were determined systematically from experiments on a
cast 319-T6 aluminum with small and large SDASs. The capabilities of the constitutive model were checked by the comparisons
of simulations to experiments in the small-strain regime (<0.005). The results show that the model provides successful simulations
for material response after thermal exposure at high temperature and cyclic transient stress-strain behavior. The causes of
mechanical behaviors at the macro scale are discussed based on microstructural changes during thermal exposure. 相似文献
43.
Berk Ozsayin Emre Yilmaz Medine Ispir Hasan Ozkaynak Ercan Yuksel Alper Ilki 《Construction and Building Materials》2011,25(10):4017-4024
The mechanical characteristics of infill walls retrofitted with carbon fiber reinforced polymer (CFRP) sheets are really important for the realistic prediction of seismic performance of the vulnerable reinforced concrete (RC) frames retrofitted through CFRP strengthened infill walls. In this study, 36 hollow brick wall specimens were tested either under uniaxial compression or diagonal tension before and after retrofitting externally with CFRP sheets. The test parameters are the dimensions of the walls, the orientation of holes of bricks, the type of mortar, the amount of CFRP sheets and the details of strengthening application. At the end of the tests, a significant contribution of CFRP sheets on the mechanical characteristics of hollow brick walls was observed in terms of several important structural design parameters such as Young and shears moduli, axial and shears strengths as well as the deformation capacity. Finally, the strength and deformability characteristics of the walls and frames retrofitted with CFRP sheets were predicted analytically. The predictions were in good agreement with the experimental data. 相似文献
44.
Swage casting is a new casting technique which combines the advantages of squeeze, centrifugal and semi-solid casting methods. In this new casting method, components with one rotating axis can be produced on a swage casting machine from molten metal in a one-step operation. A shape like a “bomb-body” is chosen to demonstrate the advantages of this new method by using A380 Al–Si–Cu alloy. The same alloy is also cast with centrifugal and squeeze casting methods. In this study, the swage casting method and its features are briefly described. The final microstructures, mechanical properties and amount of porosity of the cast pieces produced by squeeze, centrifugal and swage casting methods are compared. Swage cast pieces showed a different composition of microstructure that consists of fine dendritic particles at the chill ends and a mixture of spherical and rosette shaped particles at the core. The swage cast pieces also have a slightly higher mechanical strength as indicated by tensile strength and Brinell hardness values. 相似文献
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47.
Multirelational k-Anonymity 总被引:1,自引:0,他引:1
Nergiz Mehmet Ercan Clifton Christopher Nergiz Ahmet Erhan 《Knowledge and Data Engineering, IEEE Transactions on》2009,21(8):1104-1117
k-Anonymity protects privacy by ensuring that data cannot be linked to a single individual. In a k-anonymous data set, any identifying information occurs in at least k tuples. Much research has been done to modify a single-table data set to satisfy anonymity constraints. This paper extends the definitions of k-anonymity to multiple relations and shows that previously proposed methodologies either fail to protect privacy or overly reduce the utility of the data in a multiple relation setting. We also propose two new clustering algorithms to achieve multirelational anonymity. Experiments show the effectiveness of the approach in terms of utility and efficiency. 相似文献
48.
H. Huseyin Ozturk 《国际能源研究杂志》2005,29(10):937-944
This paper presents an experimental determination of energy requirement for greenhouse heating. The overall heat loss coefficient, heat input, the control factor for air‐tightness, the rate of heat loss and the thermal screen effectiveness were calculated. The relationships between the overall heat loss coefficient and the wind speed, and the outside temperature were modelled, including the measured and calculated values. It was found that the thermal screen effectiveness was 16 and 19.8% for the polyethylene (PE) and polyester screens, respectively. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
49.
This paper is concerned with the static and dynamic bifurcation phenomena exhibited by a nonlinear autonomous system in the vicinity of a double-zero eigenvalue. It is demonstrated analytically that such a coincident critical point is often located on the intersection of the divergence and flutter boundaries of the system. The analysis is performed via a new 'unification technique' which is based on an intrinsic perturbation procedure. The new approach is capable of yielding information about stability of solutions as well as incipient and secondary bifurcations. Indeed, the stability properties of the system and secondary Hopf bifurcations are discussed conveniently, and explicit results concerning post-critical solutions are presented. An illustrative example is analysed. 相似文献
50.
Superalloys are used in aggressive atmospheres in aero-engines and land-base gas turbines. IN738LC is an important superalloy
used in gas turbines. Strengthening Ni3(Al,Ti,Nb) type precipitate phase in this superalloy goes through size and morphological changes with time and temperature.
Experimental observations suggest precipitate motion as a whole in the matrix leading to agglomeration of nearby precipitates
for coarsening, which is in contrast to the traditional Ostwald ripening. Likewise, contrary to the conventionally accepted
view of constant activation energy, experimental data in this study indicate varying activation energy, which causes coalescence
and relates to the precipitate size in the form of an increasing polynomial. 相似文献